Measurement of the Neutron-Induced Fission Cross Section of Neptunium-237 Relative to Uranium-235 from 20 keV to 30 MeV

We have measured the fission cross-section ratio of ²³⁷Np to ²³⁵U as a function of neutron energy from 20 keV to 30 MeV using ionization fission chambers, the threshold cross-section method, and the time-of-flight technique at the Lawrence Livermore National Laboratory 100-MeV electron linear accelerator. The measured cross-section ratio, averaged over the neutron energy interval from 1.75 to 4.00 MeV, is 1.294 ± 0.019.